It is known in the prior art to manufacture thermostatic switches comprising a housing of electrically nonconductive material having a cap of nonconductive material attached thereto so as to provide a closed chamber, a fixed contact member within the chamber, and a movable contact also within the chamber normally in engagement with the fixed contact to close the switch, and a transfer pin projecting through the cap into the chamber for engagement with the movable contact to force the latter away from the fixed contact to open the switch. Movement of the transfer pin is controlled by a bimetallic disc mounted to the cap exteriorly of the chamber so as to engage the protruding end of the transfer pin to move the latter axially to disengage the movable contact from the fixed contact responsive to a predetermined temperature condition. The switch as thus constructed makes or breaks the flow of current between two live conductors, one of which is electrically connected to the fixed end of the movable contact and the other of which is connected to a terminal which is in turn connected to the fixed contact.
There are, however, situations wherein only one live conductor is used to pass current to the switch, that is, the switch is connected to ground rather than having a second live conductor which carries away the current. If such is the situation, it would be necessary to electrically shunt the terminal which extends from the fixed contact to the metallic peripheral cap that is normally used to maintain the housing, cover, and disc in assembled relation, it being understood that the cap is connected to ground by virtue of the mounting of the switch assembly in a member or device that is in turn grounded. It is obviously impractical to connect such a shunt between the fixed contact and the cap member and so thermostatic switches have been specifically designed for grounded application. For example, the bimetallic disc may be provided with a contact member centrally secured to its upper surface whereby when the disc snaps upwardly to its closed position, the contact engages a fixed contact to close the switch. Since the peripheral edge of the bimetallic disc is retained by and hence is in engagement with the metallic cap, the switch will automatically be grounded because, when the switch is closed, current will flow through the disc to the cap to effect grounding.
The problem with this type of arrangement is that the flow of current through the bimetallic disc generates heat which adversely affects the thermostatic action of the switch. For example, the heat so generated causes the switch to prematurely close or open, as the case may be. The purpose of the present invention is to design a grounded thermostatic switch of improved design so as to make possible continued use of standard parts of a conventional thermostatic switch as much as possible and so as to eliminate the flow of current through the bimetallic element, thus eliminating adverse effects in the thermal accuracy of the switch, as would happen in the grounded switch referred to above.